This invention relates generally to a process for preparing water-soluble cationic polymers from non-ionic acrylamide monomers, dialkylaminoalkyl acrylate quaternary cationic monomers, and a waste stream which is produced as a result of the transesterification reaction used to produce the cationic monomer. More particularly, the present invention relates to the use of an azeotropic waste stream which is generated and removed during the transesterification reaction between a dialkylamino alcohol and an acrylate, which is the primary step in the preparation of the cationic monomers.
Cationic water-soluble polymers containing dialkylaminoalkyl acrylate quaternaries are well-known. Such polymers have found a wide variety of uses, for example as flocculants in the mining and paper industries and especially in sewage treatment for sludge dewatering. In view of the large quantities of these polymers used in each of these applications, there is a continuing need to develop more efficient polymer compositions and methods of preparing them.
Furthermore, the use of both the quaternized and unquaternized compounds in other applications, i.e. paints, textiles, and sizes, is growing rapidly. As such, the amount of azeotropic waste stream being produced is increasing and there is an increasing need to develop uses for it. The present invention, which resulted from research to develop improved cationic polymers, provides a new and valuable commercial use for the waste stream.
The present invention is based upon replacing a portion of the non-ionic acrylamide content of a cationic polymer with a waste stream which has been azeotropically stripped off during and after a transesterification reaction which has been used to prepare the cationic monomer. The cationic monomers useful in the present invention and from which the waste stream is produced include those of the formula: ##STR1## wherein R is hydrogen or methyl, R.sup.1 is lower alkylene, and R.sup.2, R.sup.3, and R.sup.4 are each lower alkyl groups as defined further below. These monomers are conventionally prepared by a transesterification reaction between an excess of a lower acrylate or methacrylate of the formula: ##STR2## wherein R.sup.5 is lower alkyl, and a dialkylamino alcohol of the formula: ##STR3## in the presence of catalysts such as metal alkyls, metal alkoxides or organic quaternaries, followed by a quaternization reaction with such as methyl chloride or dimethyl sulfate. Some recent patents related to improving the transesterification process include U.S. Pat. Nos. 3,784,566, 4,074,062, 4,202,990, 4,281,175, 4,301,297, and 4,543,422. In the reaction, the alcohol R.sup.5 OH is formed as a byproduct and it is removed, along with excess starting acrylate or methacrylate and substantial amounts of unquaternized dialkylaminoalkyl acrylate, trace amounts of acrylic or methacrylic acid, and some dialkylamino alcohol starting material, generally as an azeotrope by vacuum distillation and generally in the presence of polymerization retarders/inhibitors. Some recent disclosures relating to the distillation include such as U.S. Pat. Nos. 3,959,358 and 4,369,097. This distillation is generally performed at high efficiency and with a high reflux ratio, i.e. 2 to 10 or more. The only present uses for the azeotropic waste stream are either (i) to separate out the R.sup.5 alcohol by a further distillation to recover a stream containing about 90% methyl acrylate or methacrylate which can then be recycled in small amounts (along with other associated by-products, i.e. the other 10%) into subsequent transesterfication reactions or (ii) to burn the stream for its fuel value. Waste stream recycling is normally kept to a minimum in order to avoid a build-up of adverse by-products.
To complete the preparation of the cationic monomer, the transesterified material is then quaternized with such as methyl chloride or dimethyl sulfate, generally in the presence of solvents, such as water or ketones, and/or catalysts. Some recent patents directed to the quaternization reaction include U.S. Pat. Nos. 3,948,979, 4,169,208, 4,180,519, 4,362,890 and 4,520,210. The quaternized cationic monomer is then cleaned up to produce the very high purity monomer which is needed for polymerizations. Some recent patents dealing with post-treatment purifications include U.S. Pat. No. 4,614,827 and Jap. Kokai Patent No. SHO 60 (1985)-48955.
The presently commercially utilized cationic monomers have a purity of at least 99.5 percent though generally the purity is 99.8 percent or higher.
It is thus apparent that although the art is aware that cationic monomers must be highly pure to be reproducibly polymerized and, therefore, expensive and time-consuming purification steps are needed in preparing the cationic monomers, there has been no attempt heretofore to develop a practical use for either of the primary waste streams which result from the purification steps.
It is accordingly an object of the present invention to incorporate, into a polymerizable mixture, a minor amount of a waste stream which is produced by azeotropic stripping during and after a transesterification cationic-monomer-forming reaction, to produce water-soluble cationic polymers having substantially lower raw material costs but at least equivalent polymerization and performance profiles to conventionally prepared polymers.
It is a further object to utilize the azeotropic waste stream in water-in-oil emulsion polymerizations to produce particles of water-soluble polymers which, when used in dewatering-type applications exhibit superior performance.
These and other objects will become apparent from the following detailed description of the invention.